Does anyone know what is this?

Last day I bought 5 ember tetras. One of them has a bubble in it's mouth, which I noticed only after I acclimated it to my tank. It looks like a chewing gum bubble.. PLease let me know if it is a disease . If it is , what is the cure?

 

I have never seen a disease like this. It maybe a gas bubble disease.
Experts can help you. @Coradee please help out.

 

I've never seen anything like that either sorry, hopefully someone with more knowledge of it can chime in

 

can it be mouth fungus?

I searched and found that the closest thing is mouth fungus

 

I think it is Dermosporidia